What is the best way to extract the initial n rows of a JSON String array using JavaScript?

Question

What is the best way to extract the initial n rows of a JSON String array using JavaScript?

Currently, I am working with a JSON string that represents an array.

arrayString = "[
  { fName: 'John', lName: 'Doe'},
  { fName: 'Jane', lName: 'Doe'},
  { fName: 'Josh', lName: 'Doe'},
  { fName: 'Jack', lName: 'Doe'},
  { fName: 'Jill', lName: 'Doe'},
  { fName: 'Josh', lName: 'Doe'},
  { fName: 'Jean', lName: 'Doe'},
  { fName: 'Jake', lName: 'Doe'},
  { fName: 'Judy', lName: 'Doe'},
  { fName: 'Jery', lName: 'Doe'},
]";

I am facing an issue where parsing all the elements in one go using .json() method is causing high memory consumption due to the sheer volume of data. To address this, I am looking for a solution to parse only the first n rows from the array, mimicking client-side pagination for retrieving data efficiently from the string. However, it's important to note that I have no control over how this extensive dataset is sent from the server.

javascript json parsing ecmascript-6 pagination

Answer 1

Answer №1

This issue could be addressed server-side through proper API design, but another approach is to consider utilizing range requests. By using range requests, specific portions of the data can be requested, avoiding potential corruption in the final fragment and ensuring that the client does not unnecessarily store large amounts of data.

If you prefer parsing segments of the complete dataset already stored on the client side, ES6 (ES2015) generators offer an ideal solution:

/**
 * This generator yields a specified number of records at each iteration.
 * @param {string} data          The data from which to extract records.
 * @param {number} n             Number of objects per yield.
 * @yield {string} Array containing the specified number of objects represented as a valid JSON string.
 */
function* getNRecords(data, n) {
  let index = 0;
  while (index < data.length) {
    let result = data.substring(index).split('}', n).join('}');
    
    result = result.endsWith('}]') ? result : result + '}]';
    result = index > 0 ? '[' + result.trim() : result; // Ensure it starts with '['
    
    index += result.length;
    yield result;
  }
}

/* === EXAMPLE === */

const exampleData = '[{a: 1, b: 2}, {c: 3, d: 4}, {e: 5, f: 6}, {g: 7, h: 8}]';
const batchSize = 3;

for (let nRecords of getNRecords(exampleData, batchSize)) {
  console.log(nRecords); // Additional parsing can be done here
}

The extraction of up to N objects occurs in this line:

data.substring(index).split('}', n).join('}');

.

Answer 2

This issue could be addressed server-side through proper API design, but another approach is to consider utilizing range requests. By using range requests, specific portions of the data can be requested, avoiding potential corruption in the final fragment and ensuring that the client does not unnecessarily store large amounts of data.

If you prefer parsing segments of the complete dataset already stored on the client side, ES6 (ES2015) generators offer an ideal solution:

/**
 * This generator yields a specified number of records at each iteration.
 * @param {string} data          The data from which to extract records.
 * @param {number} n             Number of objects per yield.
 * @yield {string} Array containing the specified number of objects represented as a valid JSON string.
 */
function* getNRecords(data, n) {
  let index = 0;
  while (index < data.length) {
    let result = data.substring(index).split('}', n).join('}');
    
    result = result.endsWith('}]') ? result : result + '}]';
    result = index > 0 ? '[' + result.trim() : result; // Ensure it starts with '['
    
    index += result.length;
    yield result;
  }
}

/* === EXAMPLE === */

const exampleData = '[{a: 1, b: 2}, {c: 3, d: 4}, {e: 5, f: 6}, {g: 7, h: 8}]';
const batchSize = 3;

for (let nRecords of getNRecords(exampleData, batchSize)) {
  console.log(nRecords); // Additional parsing can be done here
}

The extraction of up to N objects occurs in this line:

data.substring(index).split('}', n).join('}');

.

What is the best way to extract the initial n rows of a JSON String array using JavaScript?

Answer №1

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